Various techniques are known for installing cable in duct or other conduit, which can be underground, above ground or in buildings. Sometimes the underground duct is known as "innerduct." A first technique is to pull the cable through conduit with a previously positioned wire or string attached to a lead end of the cable.
The use of high speed moving air to drag a lightweight and flexible optical fiber member through the conduit is also known, such as described in U.S. Pat. No. 4,691,896, to Reeves et al. According to Reeves et al., the high speed air creates a fluid drag force distributed along the optical fiber member in order to pull the optical fiber member through the conduit.
U.S. Pat. Nos. 4,850,569 and 4,934,662 to Griffioen et al. describe combining high speed air flow with a pushing force applied at the entry end of the conduit to install the cable. U.S. Pat. Nos. 5,197,715 and 5,474,277 to Griffioen further describe the use of a leaky missile attached to the lead end of the cable which adds a tension force on the lead end of the cable, in addition to the motive forces applied to the cable via the high speed moving air.
The use of pressurized air in combination with a sealed missile, parachute or other device for creating a pressure difference at the lead end of the cable is also known. The pressure difference creates a pushing force on the missile or other device, which pulls the lead end of cable through the conduit.
Various concerns arise when cable is installed in conduit. One concern is the ease of installation. A further concern is avoidance of damage to the cable during installation. Damage can occur in a variety of ways including: 1) crushing the cable with the installation equipment in the diametral direction; 2) causing the cable to have bending damage or column damage (may be referred to as "accordion damage") due to an excessive force applied in the longitudinal direction; and 3) damaging the protective cable jacket, such as by wearing, shredding or cutting the outer protective layer. Another concern is to minimize the amount of time needed to install the cable. Also, there is a concern to avoid splices in the cable as much as possible. Splices are time consuming to make, and may lead to a decrease in cable performance. Therefore, it is desirable to install the longest continuous length of cable possible to reduce the number of splices needed for the desired cable run.
There is a need in the prior art for further systems and methods which address the above-identified concerns, and other concerns.